This invention relates in general to electrophotographic imaging members and, more specifically, to positively and negatively charged electrophotographic imaging members having a single electrophotographic photoconductive insulating layer and processes for forming images on the member. More specifically, the present invention relates to a singled layered photoconductive imaging member containing a charge generation layer or photogenerating layer comprised of a Type IV titanylphthalocyanine (TiOPC(IV)) component dispersed in a matrix of a hole transporting and an electron transporting binder. The electrophotographic imaging member layer components, which can be dispersed in various suitable resin binders, can be of various thickness, however, in embodiments, a thick layer, such as from about 5 to about 60, and more specifically from about 10 to about 40 microns, is selected. This layer can be considered a dual function layer since it can generate charge and transport charge over a wide distance, such as a distance of at least about 50 microns. Also, the presence of the electron transport components in the photogenerating layer can enhance electron mobility and thus enable a thicker photogenerating layer, and which thick layers can be more easily coated than a thin layer, for example, from about 1 to 2 microns thick.
A number of electrophotographic imaging members are multi-layered imaging members comprising a substrate and a plurality of other layers, such as, a charge generating layer and a charge transport layer. These commercial multi-layered imaging members also often contain a charge blocking layer and an adhesive layer between the substrate and the charge generating layer. Further, an anti-plywooding layer may be needed. This anti-plywooding layer can be a separate layer or be part of a dual function layer. An example of a dual function layer for preventing plywooding is a charge blocking layer or an adhesive layer which also prevents plywooding. The expression “plywooding”, as employed herein, refers in embodiments to the formation of unwanted patterns in electrostatic latent images caused by multiple reflections during laser exposure of a charged imaging member. When developed, these patterns resemble plywood. These multi-layered imaging members are also costly and time consuming to fabricate because of the many layers that must be formed. Further, complex equipment and valuable factory floor space are required to manufacture these multi-layered imaging members. In addition to presenting plywooding problems, the multi-layered imaging members often encounter charge spreading which degrades image resolution.
One problem encountered with multilayered photoreceptors comprising a charge generating layer and a charge transport layer is that the thickness of the charge transport layer, which is normally the outermost layer, tends to become thinner due to wear during image cycling. The change in thickness causes changes in the photoelectrical properties of the photoreceptor. Thus, to maintain image quality, complex and sophisticated electronic equipment and software management are usually necessary in the imaging machine to compensate for the photoelectrical changes, which can increase the complexity of the machine, cost of the machine, size of the footprint occupied by the machine, and the like. Without proper compensation of the changing electrical properties of the photoreceptor during cycling, the quality of the images formed can degrade because of spreading of the charge pattern on the surface of the imaging member and a decline in image resolution. High quality images can be important for digital copiers, duplicators, printers, and facsimile machines, particularly laser exposure machines that demand high resolution images. Moreover, the use of lasers to expose conventional multilayered photoreceptors can lead to the formation of undesirable plywood patterns that are visible in the final images.
Attempts have been made to fabricate electrophotographic imaging members comprising a substrate and a single electrophotographic photoconductive insulating layer in place of a plurality of layers such as a charge generating layer and a charge transport layer. However, in formulating single electrophotographic photoconductive insulating layer photoreceptors many problems need to be overcome including charge acceptance for hole and/or electron transporting materials from photoelectroactive pigments. In addition to electrical compatibility and performance, a material mix for forming a single layer photoreceptor should possess the proper rheology and resistance to agglomeration to enable acceptable coatings. Also, compatibility among pigment, hole, electron transport molecules, and film forming binder is desirable. As utilized herein, the expression “single electrophotographic photoconductive insulating layer” refers in embodiments to a single electrophotographically active photogenerating layer capable of retaining an electrostatic charge in the dark during electrostatic charging, imagewise exposure and image development. Thus, unlike a single electrophotographic photoconductive insulating layer photoreceptor, a multi-layered photoreceptor has at least two electrophotographically active layers, for example at least one charge generating layer and at least one separate charge transport layer.